The present invention relates to improved curable silicone compositions. More particularly, the present invention relates to curable silicone coating compositions comprising SiO.sub.2 -based resins and a polydiorganosiloxane.
Keil, U.S. Pat. No. 3,527,659, discloses a release agent for substrates consisting of a dimethylpolysiloxane-based formulation which is curable to an elastomer and a copolymer of R.sub.3 SiO.sub.1/2 and SiO.sub.2 units having no more than 0.7 weight percent silicon-bonded hydroxyl groups. Adhesive release force of the release agent is said to increase as the amount of copolymer in the release agent is increased.
Brady, U.S. Pat. No. 3,627,851, discloses curable compositions consisting essentially a vinyl- or silanol-containing polydiorganosiloxane gum, a benzene-soluble copolymeric siloxane consisting of dimethylhydrogensiloxy units, trimethylsiloxy units and SiO.sub.2 units and a platinum-containing catalyst.
Flannigan, U.S. Pat. No. 3,722,247 discloses organopolysiloxane resins containing R.sub.3 SiO.sub.1/2 units and SiO.sub.2 units, along with RHSiO units and/or HSiO.sub.3/2 units which are suitable for a wide variety of uses, such as for modifying siloxane paper-treating compositions, for preparing other reactive resins and for crosslinking room temperature curing elastomer-forming compositions.
A principal disadvantage of the compositions of the art which comprise a SiO.sub.2 -based resin is that the resin is a solid at room temperature and requires the use of a solvent to aid its mixing with the other components of the compositions. However, it is currently highly desirable to prepare solventless silicone compositions so that emissions of solvents into the atmosphere during their preparation and use can be avoided.